High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al. U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
The most commonly employed polyester prepared by these teachings, poly(ethylene terephthalate), has not been widely accepted for use as a molding resin, however, until only fairly recently, because of its relative brittleness in thick sections when crystallized from the melt. The problem was overcome by varying the crystal texture, e.g., by using two step molding cycles or by including nucleating agents, and by molecular weight control. This permitted the marketing of injection-moldable poly(ethylene terephthalates) which typically, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, and lower surface friction. Solvent resistance is outstanding, making such compositions uniquely useful in the automotive and aircraft industries. Among the disadvantages of poly(ethylene terephthalate) in molding compositions are the relatively high cost of manufacture (because of the need to control crystal texture), a relatively low degree of moisture resistance, a rapid burning rate and a tendency to drip flaming resin while burning.
Surprisingly, it has been found that the need to employ nucleating agents or two stage molding cycles to avoid brittleness in thick molded sections is obviated if higher homologs of poly(ethylene terephthalate) are mixed with it or substituted for it. For example, within the broad disclosure of the Whinfield et al. and Pengilly patents there exists a family of polyester resins which are normally crystalline and which rapidly crystallize from the melt. These crystallize so rapidly, in fact, that standard injection molding cycles can be used and there is no need to include nucleating agents in the formulation. Parts molded from such polyesters, in contrast to those of poly(ethylene terephthalate) alone, have good impact strength in thick sections.
The rapidly crystallizable higher homologs comprise generally polyester resins which are poly(alkylene terephthalates, isophthalates or mixed terephthalates and isophthalates), wherein the alkylene groups contain from 3 to 10, and especially 3 to 6, carbon atoms.
Simultaneously with the development of injection molding grades of poly(ethylene terephthalate) resins, fiber glass reinforced compositions were also provided. See Furukawa et al. U.S. Pat. No. 3,368,995. These injection moldable compositions provided all of the advantages of unfilled polyesters and, also, because of the glass reinforcement, the molded articles had higher rigidity, yield strength, modulus and impact strength.
However, because they used poly(ethylene terephthalate) the Furukawa et al compositions required two stage molding or the use of nucleating agents to avoid embrittled thickly molded sections. Moreover, they retained the disadvantages inherent in polyesters generally, having a relatively high cost of manufacture and formulation, and low degree of moisture resistance, high flammability and a tendency to drip while burning.
Although substitution of the rapidly crystallizable higher homologs of poly(ethylene terephthalate) would be expected to overcome the need for two stage molding cycles or nucleating agents, such compositions, in common with those described by Furukawa et al., would still be expensive, unstable to moisture, flammable and would drip while burning. While resistant to gasoline, jet fuels, hydraulic fluids and the like, such compositions would be of limited utility in the automotive and aircraft industries because of their flammability. On the other hand, because of moisture sensitivity, their use in kitchens, laundries, on shipboard, and the like, would be limited.
It has now been discovered that a new family of composites are provided if the rapidly crystallizable polyesters are combined with at least one other polymer and a reinforcing filler. Without the filler component, great difficulty is experienced in processing the blend of two polymers. Surprisingly, as little as 1% by weight of reinforcing filler, such as glass, provides unexpected improvement in processability, surface appearance and physical properties.
It is a primary object of this invention to provide reinforced compositions in which the properties of one of the polymeric components are used to enhance the properties of the second polymeric component.
Merely by way of illustration, the hydrolytic stability of poly(1,4-butylene terephthalate) will be enhanced according to this invention by forming a reinforced combination with polyolefins and the strength, rigidity and resistance to heat distortion of polyolefins will be improved by forming a reinforced combination with poly(1,4-butylene terephthalate).
It is surprising and unexpected to find that such polyesters form useful combinations with a remarkably broad range of polymers. Usually, when such mixtures including at least one highly crystallizable polymer are molded and cooled, they are non-uniform and tend to delaminate. In contrast to the expected behavior, rapidly crystallizable polyesters have now been found readily to form composites with crystalline, amorphous and partially crystalline and partially amorphous polymers and, after reinforcement, such new compositions are easily moldable and extrudable into articles which are uniform and which do not delaminate. All of these characteristics of the new compositions of this invention indicate that an intercrystalline or crystalline-amorphous combination is formed between the polyester and the second co-blended polymer. In addition, the enhancement in strength of the composite is evidence that the reinforcing filler, e.g., a metal, ceramic, silica, quartz, asbestos, silicate, titanate, carbon black, clay, glass, and the like, is unexpectedly and strongly bonded into the combination. Moreover, the reinforcing filler is essential ingredient in the combination to obtain the required physical properties and processability.
In addition to the other principal objects mentioned above, it is a further object of this invention to provide compositions exhibiting improved resistant to distortion by heat, even at very low levels of reinforcement, improved surface appearance, improved processability and other commercially significant properties.
It is a further object of this invention also to provide the novel reinforced compositions in flame retardant and non-dripping embodiments.